Modern day information is commonly stored in magnetic disk drives that include a rotating magnetic disk and a slider containing one or more magnetic head assemblies that house read and write heads that are suspended over the disk by a swinging suspension arm. When the disk rotates, air flows underneath the slider and causes it to lift off and ‘fly’ over the surface of the rotating disk, allowing for the magnetic heads to be employed via processing circuitry to read and write magnetic impressions to and from the rotating disk.
The write head includes at least one coil, a write pole, and one or more return poles. When current flows through the coil, it induces a magnetic field that emanates from the write pole into the disk. The magnetic field is sufficiently strong that it locally magnetizes a portion of the magnetic media, thus allowing for data bits to be recorded onto the disk. After passing through the magnetic layer, the magnetic field travels through the rest of the disk and completes its path by returning to the return pole of the write head.
Once a data bit is recorded onto the disk, its magnetic state can be read with a magnetoresistive sensor, such as giant magnetoresistive (GMR) or a tunnel junction magnetoresistive (TMR) sensor that has a measurable electrical resistance that changes in response to the magnetic field state of the recorded data bit.
This read/write method is the recording technique typically implemented in conventional perpendicular magnetic recording (PMR). However, as data density needs increase and data bits are made smaller and packed closer together, they become thermally unstable and prone to demagnetization. One way to circumvent this problem is to make the recording media more magnetically stiff, i.e., have a higher magnetic anisotropy. However, ‘stiffer’ media also require higher recording magnetic fields, something which is in itself a limitation since in order to record smaller data bits, the pole size also needs to be reduced, and this in turn reduces the strength of the magnetic field that can be delivered to the disk.
A solution to this challenge is to use heat assisted magnetic recording (HAMR) in which data bits are defined by locally heating the media through the use of a near field thermal transducer (NFT) just at the location on the disk that is to be recorded. The heating process temporarily lowers the magnetic anisotropy of the media, thus ‘softening’ it and allowing it to be recorded with the write pole at write fields that would otherwise be too weak to induce magnetization. Then, after the data has been written, as the disk spins past the NFT, the media cools, causing the anisotropy of the media to rise again, thereby ensuring that the media ‘freezes in’ the magnetic state of the recorded data bit.